It is well known that farming shellfish, mollusks and fry requires the use of marine chlorella type algae of high nutritive value. These algae have a high polyunsaturated fatty acid content. The fatty acids are essential acids, since these acids are not synthesized by the animals themselves. Accordingly, these fatty acids have to be provided in an assimilable form.
In order to replace the marine chlorella type algae in the best possible way, the incorporation of fish oils, and mainly of cod-liver oil which is especially high in polyunsaturated fatty acids, into some compositions has already been contemplated.
It has already been proposed to enrich bakers' yeast with fish oil, with a view to increasing the dietetic value of the rotifer which feeds on it. The term "rotifer", as used herein, shall mean any of a class of minute, usually microscopic, but many-celled aquatic invertebrate animals having the anterior end modified into a retractile disk bearing circles of strong cilia that often give the appearance of rapidly revolving wheels. In the food chain, the rotifers feed on the yeasts while the fry feed on the rotifers. However, in this application, it is clearly indicated that the yeast must absolutely remain live because otherwise, oil assimilation will not occur and such would lead to a reduction in the nutritive value of the yeast. Additionally, these methods state that the yeast should not be dried because drying would lead to disadvantageous alterations thereof.
On the basis of these demonstrations, it is obvious that the possibilities of application of such a product are largely limited, because most often the yeasts must be freshly prepared and must remain in solution in order to preserve all its properties. In addition, it is known that such products undergo oxidation and even after only eight days of storage, the appearance of mold was observed. Accordingly, these yeast compositions are not suitable for long term storage. It would therefore be advantageous if a dried yeast which would have the same nutritional properties as the marine chlorella type algae, but which could be stored without the oil being oxidized or the appearance of mold being observed were available.
The present invention provides a process which makes it possible to prepare new yeasts containing high polyunsaturated fatty acid oil, which yeasts can be stored without difficulty.